The dynamic aspect of vacuum in quantum field theory
has extensively been explored so far in light of the reheating process
after the inflation in the early Universe, that is called the preheating
[1]}, [2]}, [3]}, [4]}, [5]} (for reviews, see e.g., [5]}, [7]}, [8]}, [9]}).
The oscillating background field of the inflaton induces the nonadiabatic state for other coupled species. It drives the nonperturbative particle production, and the amount is exponentially amplified by the parametric resonance similar to a swing with a pumping oscillator.
The mechanism of preheating is applied to interesting variant scenarios:
the production of massive particles heavier than the inflaton[10]}, [11]}, [12]}, [13]};
the preheating due to the alternative field instead of the inflaton
[14]}, [15]}, [16]}, [17]}, etc.
